Some vehicles include engines that may be partially deactivated to increase the fuel efficiency by reducing the effective displacement of the engine during select operating conditions. As such, some engines may be referred to as having a variable displacement capability, whereby combustion in one or more cylinders of the engine may be temporarily deactivated or discontinued while other cylinders of the engine continue to carry out combustion. Where increased engine output is requested by the vehicle operator, the deactivated cylinders may be activated by once again performing combustion to thereby increase the effective engine displacement and provide the requested engine output to the vehicle operator.
The inventors of the present disclosure have recognized a disadvantage with the above approach. As one example, the inventors have recognized that during some conditions the above approach may result in frequent transitions from a deactivated state of the cylinders to an activated state where combustion is performed. These transitions may increase noise, vibration, and harshness (NVH) of the engine that may be perceived by the vehicle operator. Additionally, fuel efficiency may be reduced where frequent transitions between active and deactivated states are performed by the engine. As such, engines having this variable displacement capability may exhibit only limited fuel efficiency improvements while perceived drivability of the vehicle from an operator's perspective may be reduced.
As a non-limiting example, at least some of the above issues may be addressed by a method of operating a vehicle propulsion system, comprising: operating an engine to produce an engine output; transferring the engine output to one or more drive wheels via a transmission; responsive to a first condition, varying torque supplied to the drive wheels by adjusting a relative number of combusting cylinders and deactivated cylinders of the engine; and responsive to a second condition, varying the torque supplied to the drive wheels by adjusting a number of strokes performed by the combusting cylinders per combustion cycle while shifting the transmission between different gear ratios.
Since the power density of the engine may be increased by transitioning the engine from the four stroke cycle to the two stroke cycle, the vehicle operator's requested engine output may be met while maintaining the deactivated cylinders in the deactivated state rather than initiating combustion in the deactivated cylinders. Additionally, coordination of engine operation with the transmission state may enable further reduction in the number of transitions between active and deactivated cylinder states.